Laser beam brazing of aluminum alloys in XHV-adequate atmosphere with surface deoxidation by ns-pulsed laser radiation

Abstract

Laser beam brazing is an established manufacturing process due to its low heat input and esthetically appealing seams. However, brazing of materials with high oxygen affinity, such as aluminum alloys, requires the removal of surface oxides prior to the brazing process, commonly through the application of chemical fluxes that may be harmful to the environment and to health. The approach presented here dispenses with the use of fluxes and involves oxide layer removal by means of ns-pulsed laser radiation within an atmosphere that is adequate to an extreme high vacuum (XHV) in regard to the oxygen content. By doping the process gas with monosilane (SiH4), an oxygen content equivalent to an extreme high vacuum with an oxygen partial pressure below 10−20 mbar is realized. Hence, a subsequent reoxidation is actively prevented so that wetting of the base material by the filler material and consequent diffusion processes are enabled. The wetting angle between filler material and material is used to evaluate the effectiveness of laser-based deoxidation under an XHV-adequate atmosphere.

Investigations into Flux-Free Plasma Brazing of Aluminum in a Local XHV-Atmosphere

“…The results of the oxygen measurement show that XHV-adequate oxygen concentrations can locally be achieved by adding silane to the arc process zone. This is similar to earlier results in related work [ 23 , 24 ]. The spectroscopic analyses are suitable to further elaborate the mechanisms leading to the previously found oxygen reduction.…”

“…Considering that the natural oxide layer on aluminum is only 2 nm thick, the reduction effect achieved in the present study is more than sufficient. Previous studies already showed that when the oxide layer is removed and the joining atmosphere prevents re-oxidation, wetting of the surface is no challenge anymore, and flux-free brazing is possible [ 7 , 12 , 24 ]. This effect can be exploited for the plasma process, too.…”

“…Still, the thermodynamical consideration indicates that adding silane into a thermal plasma could theoretically reduce the thickness of an aluminum oxide layer. Prior studies already showed that very low oxygen contents in a process atmosphere could be achieved using silane [ 23 , 24 ]. If the oxide layer is removed by an ns-pulsed laser, a silane-doped atmosphere can prevent re-oxidation [ 24 ].…”

“…Prior studies already showed that very low oxygen contents in a process atmosphere could be achieved using silane [ 23 , 24 ]. If the oxide layer is removed by an ns-pulsed laser, a silane-doped atmosphere can prevent re-oxidation [ 24 ].…”

Oxygen‐Free Production—From Vision to Application

“…Aman et al illustrate that laser beam brazing of aluminum alloys in an oxygen‐free atmosphere efficiently prevents reoxidation, while at the same time facilitating the removal of the oxide layer, thereby making the use of flux obsolete. [ 60 ] In their work, Aman et al used a setup of two laser beam sources, a pulsed (pw) laser beam source for removal of the oxide layer with pulses in the nanosecond regime and a continuous wave (cw) laser beam source for the brazing process. The process was performed inside a glove box, which was filled with silane‐doped argon providing an oxygen‐free atmosphere.…”